1. Field of the Invention
This invention relates to an electronic circuit which is operable as both a frequency multiplier and a mixer and which is implemented by a semiconductor integrated circuit.,
2. Description of the Related Art
In a radio receiver or a radio transmitter, a frequency multiplier and a mixer are very often used to receive or transmit an input frequency signal (namely, a high frequency signal.) of an input frequency. Specifically, a local oscillator frequency signal of a local oscillator frequency is multiplied by the frequency multiplier into a frequency multiplied signal of a multiplied frequency. The frequency multiplied signal is sent to the mixer which is given the input or high frequency signal. The mixer mixes the high frequency signal with the frequency multiplied signal to produce, as a mixed frequency signal, an intermediate frequency signal which has an intermediate frequency equal to a sum of the input frequency and the multiplied frequency or a difference between the input frequency and the multiplied frequency.
In general, the frequency multiplier and the mixer are formed by individual electronic circuits which are implemented by semiconductor integrated circuits. This brings about an increase of a circuit size and circuit elements.
Recently, proposal has been made by the instant inventor in Japanese Patent Unexamined Publications Nos. 253409/1992 and 240904/1992 as regards an electronic circuit which is operable as both a frequency multiplier and a mixer. Such an electronic circuit comprises a transistor circuit and a constant current circuit connected in cascade to the transistor circuit. In addition, the transistor circuit is composed of first and second pairs each of which comprises transistors having collectors connected through a resistor to each other. The transistor circuit is driven by the local oscillator frequency signal while the constant current circuit is driven by the input or high frequency signal.
With this structure, it is possible to generate, through the transistor circuit, an output signal which includes a sum of a frequency component equal to twice the local oscillator frequency and the input frequency or a difference between the frequency component and the input frequency and which serves as the intermediate frequency signal. This shows that the proposed electronic circuit acts as both a local oscillator frequency multiplier and a mixing circuit, namely, a frequency doubler and a mixer.
In the meanwhile, it has been found out according to the inventor's experimental studies that a wide variety of electronic circuits can be realized to generate the above-mentioned output signal in response to the input or high frequency signal and the local oscillator frequency signal by including a certain circuit. As regards such a certain circuit, an explicit recognition is never made in the above-referenced publications. Moreover, it has been also found out that an additional function is required when the electronic circuit is to be practically used in a receiver or a transmitter.